This invention relates to brush seals. Specifically, this invention relates to the various components that form the brush seal.
Brush seals are commonly used on gas turbine engines. The brush seals typically prevent secondary flow in the engine from escaping through a gap between a stationary part (e.g. a diffuser case) and a rotating part (e.g. a turbine shaft). Brush seals can have other uses, such as sealing a gap between stationary parts of the engine.
A brush seal typically includes packs of wire bristles sandwiched between plates. The bristle packs and plates are typically welded together to form the brush seal. The brush seal must undergo heat treatment after the welding step to relieve any residual stresses. Heat treatment typically involves securing the brush seal within a fixture, then placing the fixture in an oven. The heat treatment process is time consuming and can be expensive.
The welding step transforms the discrete sub-assemblies of the brush seal into one piece. The one-piece arrangement prevents the removal of a sub-assembly without affecting or damaging the remainder of the brush seal. This means a mechanic must replace the entire brush seal during maintenance. Replacement of the entire brush seal must occur despite the fact that only one of the sub-assemblies (typically the bristle packs) needs replacement.
The bristle packs of the brush seal are expensive. The main factor influencing cost is the amount of raw material used. Each individual bristle in the bristle pack is a taken from a length of wire. A commonly used wire is a 0.002″, 0.003″, 0.004 or 0.006″ diameter cobalt alloy wire. One type of bristle pack can have approximately 5000 bristles per linear inch. This type of bristle pack clearly contains a large amount of wire. When used in a 12″ outer diameter single stage brush seal, this type of bristle pack can contain approximately 2.6 miles of wire.